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Date: Thu, 23 Apr 2015 11:00:31 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's
	description
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

Am 22.04.2015 um 12:12 hat Paolo Bonzini geschrieben:
> On 22/04/2015 11:31, Kevin Wolf wrote:
> >> Actually I liked the "foo+colo" names.
> >>
> >> These are just internal details of the implementations and the
> >> primary/secondary disks actually can be any format.
> >>
> >> Stefan, what was your worry with the +colo block drivers?
> > 
> > I haven't read the patches yet, so I may be misunderstanding, but
> > wouldn't a separate filter driver be more appropriate than modifying
> > qcow2 with logic that has nothing to do with the image format?
> 
> Possibly; on the other hand, why multiply the size of the test matrix
> with options that no one will use and that will bitrot?

Because it may be the right design.

If you're really worried about the test matrix, put a check in the
filter block driver that its bs->file is qcow2. Of course, such an
artificial restriction looks a bit ugly, but using a bad design just
in order to get the same restriction is even worse.

Stefan originally wanted to put image streaming in the QED driver. I
think we'll agree today that it was right to reject that. It's simply
not functionality related to the format. Adding replication logic to
qcow2 looks similar to me in that respect.

Kevin